Whatever the calendar may say, September is the true beginning of fashion's year. Not only does everyone return from summer rejuvenated – in July, European factories sigh after finishing manufacturing the fall clothes now in stores, while editors and stylists exhale after they close their September issues by going on summer holiday – but it's also when fashion and its media landscape take stock and make big changes, often closing chapters.

After 25 years as editor in chief, Alexandra Shulman, the much-admired British Vogue editor, has done just that: This month's issue is her last. But before closing that chapter, she wrote Inside Vogue: A Diary of my 100th Year, a collection of personal observations of the magazine's yearlong centenary preparations. The book chronicles the relentless schedule of responsibilities and obligations that have undercurrents of anxiety and exasperation, set against the background of Brexit politics and the disgrace of British retail magnate Philip Green.

"It's practically impossible to provide a logical rationale for the existence of fashion shows today," Shulman muses early on, as she catalogues the "depressing side of 21st-century journalism." At a digital meeting, Shulman learns the publication is 3-million reader views over its March target: "The figures are so huge that they're hard to consider, and it's never entirely clear what they mean in terms of revenue or real interest in the content, but on any level 38,813,597 page impressions is a massive number," she writes.

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Whatever the platform, whether it's print or Instagram, thanks to commercial pressure and advertising power, definitive judgments on fashion design have largely been banished in favour of a more conversational approach. I see it less as the erosion of authority – fashion media is not a hierarchy, it's an ecosystem – than of expertise.

The cyclicality of industry crossroads becomes apparent after reading Kate Nelson Best's The History of Fashion Journalism. The overview surveys fashion journalism's origins in the 18th-century fashion plates of Le Journal des Dames and Le Cabinet des Modes (1759 and 1785, respectively) through The Delineator (1873-1937), GQ (est. 1957), blogs (2005) and livestreaming (2010) to the present day, and concludes that the industry is in a state of flux that is no less than a revolution. If the author has any predictions, it's that the mainstream print fashion magazine may become something niche, as a high-production-value artifact filled with long-form journalism. Journalistic expertise will remain resilient, she points out, because without fashion journalism there is, arguably, no fashion – it's all just clothes.

It's worth remembering that the fashion press was originally devised as a way to celebrate, promote and sell fashion product – the underlying business agenda was set with the first use of advertorial in the 18th century. It's a relationship between press and industry that Best aptly terms copinage (friendly support). And that's now how independent influencers on Instagram, Pinterest and the like make their livings, too.

In her last chapter, which ponders the future, Best looks at the "camera culture" that social media has set in motion, in which clothing is "captured on a continuous, unregulated and unfiltered basis." But earlier in the book she notes that even this concern isn't new: The precedent to mobile and short-form social media platforms is something the Art Directors Club identified – back in 1955 – as "a transition from word thinking to visual thinking." After the Second World War, an expansive and creative period widely considered the golden age of fashion journalism, innovations like cheaper air travel enabled easier access to fashion capitals and Hasselblad and Kodak Ektachrome cameras allowed more visual and processing freedom.

Best makes the case for a relationship between the fashion media and industry as symbiotic: "As the industry changes so does its journalism, and sometimes vice versa," she writes. "Essentially, however, it remains commercial in nature." Today, social influencers and media brands maintain their relationships by necessity, the latter not just to ensure advertising but for profitable spinoff events, festivals and conferences that are necessary to keep them relevant and that require both sponsors and access to star power – key elements easily alienated by negative coverage.

Fashion brands are now drilling down the finer points of influencer marketing, which is largely divided into two camps: brand builders who create awareness versus those who drive sales. In August, influencer marketing platform Klear released findings after it studied the top brands using Instagram Stories, a feature on the app that's only a year old, to convert sales. According to Klear, the fashion industry accounts for 70 per cent of the most active brands using the feature (Urban Outfitters and Forever 21 are at the top of the list).

But to everything its season. Shulman, for example, has life after Vogue and soon starts a new monthly column with Business of Fashion. We may be in the golden age of the influencer economy, but that's provided a golden opportunity for slow fashion criticism, which is less about the clothes than a kind of cultural commentary with knowledgeable perspective that contextualizes and makes sense of it all. It's out there – and in these pages – and it's more vital than ever.

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